1. Field of the Invention
The invention generally relates to electronics. In particular, the invention relates to positioning and/or navigation with enhanced Global Positioning System (GPS) devices.
2. Description of the Related Art
The Global Positioning System (GPS) Operational Constellation nominally includes of 24 earth orbiting satellites. Each satellite radiates a spread spectrum, pseudorandom noise (PN) signal indicating the satellite's position and time. A GPS receiver tuned to receive the signals from the satellites can compute the distance to the satellites and calculate the receiver's position, velocity, and time. The receiver calculates the distance to a satellite by multiplying the propagation rate of the satellite's radio signal (the speed of light) by the time it took the signal to travel from the satellite to the receiver.
Each satellite transmits two carrier signals referred to as L1 and L2. L1 operates at a frequency of 1.57542 GHz and L2 operates at a frequency of 1.22760 GHz. Multiple binary codes induce phase modulation upon the L1 and L2 carrier signals. Each satellite in the GPS Operational Constellation transmits a unique code over the L1 and L2 carrier signals. One of the phase-modulated signals is C/A Code (Coarse Acquisition). Another phase-modulated signal is the P-Code (Precise). The P-Code is similar to the C/A Code in that it is a PN sequence which phase modulates a carrier signal. The P-Code modulates both the L1 and the L2 signals at a rate of 10.23 MHz. In an Anti-Spoofing mode, the P-Code is encrypted to produce the Y-Code to restrict access to users with the encryption key. The P-Code forms the basis for the military's Precise Positioning Service (PPS).
GPS systems provide absolute location or position information. Although relatively precise and accurate, navigation and/or positioning via GPS alone can be insufficiently accurate in the context of multiple vehicles that are traveling together. In addition, there are relatively many environments in which reception to GPS signals is relatively difficult. Examples of these environments include: indoors, such as inside a building or a parking structure, in a canyon, in a cave, in a tunnel, on a city street adjacent to relatively tall obstructions or obscurations such as buildings, in space outside the orbit of the GPS satellite constellation, such as a geosynchronous orbit, environments with interference, and the like.
In addition, conventional ultra wideband (UWB) communication techniques can be used for ranging between UWB transceivers. However, conventional techniques for UWB are relatively difficult to implement in practice, as UWB pulses are typically quite narrow pulses and are notoriously difficult to acquire and maintain acquisition. Conventional circuits used to detect UWB signals are large, expensive, and typically consume a relatively large amount of power, which can be disadvantageous in portable battery-powered devices.